Ben Goldacre’s Bad Science is an interesting read. It takes a few chapters to get used to his writing style, which at the beginning comes across as arrogant and quite condescending, but when you begin to get a flavour of what he’s up against, it falls into place. It couldn’t be any more timely considering Simon Singh’s ordeal with overreaching chiropractors.
Nothing so suspect goes on in the world of condensed matter theory? Probably not intentionally, but there is always some controversy:
“Ferromagnetism in Dilute Magnetic Semiconductors through Defect Engineering: Li-Doped ZnO” appeared in Physical Review Letters this week. Ignoring any claims of ferromagnetism (and 609 K Curie temperatures), this paper makes an astounding claim of tunable carrier concentrations in Li-doped ZnO from n-type (0-2% Li) to p-type (4-13% Li) to insulating (> 14% Li).
As a reminder, 10 atomic percent = n(Li)/n(Zn+O+Li) = 1/10, i.e. if in the form of purely substitutional Li_Zn, around one in five zinc would be replaced by Li. Even assuming a split with 50% interstitial Li ions, one in ten zinc would be replaced. This is well beyond the solubility limit. It is a brief report, so there is no detailed structural characterisation, but one would expect quite dramatic phase separation and secondary phase formation. At such high concentrations, I would also be surprised if Li ion diffusion did not contribute to the conductivity. As for their density functional calculations, the authors (and reviewers) must have failed to notice recent literature on the need for exchange-correlation functionals beyond the GGA to describe Li incorporation into ZnO or the Zn vacancy itself (e.g. 1, 2, 3, 4). If nothing else, this paper should promote some further debate.